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Vintage amp distortion

Discussion in 'Amps [BG]' started by sturoc, Jan 2, 2013.


  1. sturoc

    sturoc

    Joined:
    Dec 12, 2009
    Being the proud owner of a 1970 Acoustic amp, am hearing warm distortion as I increase volume. Love that tone but want it on demand and like higher volume clean most of the time.
    So I ask:

    Do the modern basses onboard active circuitry put out a higher voltage to where the preamps of 'vintage' gear begin to get driven too hard ?
    Thus creating distortion early in the gain structure ?
     
  2. B-string

    B-string Gold Supporting Member

    Joined:
    Nov 21, 2008
    Location:
    Lake Havasu City, Az USA
    Yes. Active basses were pretty rare in 1970.
     
  3. Tvrtko

    Tvrtko

    Joined:
    Dec 27, 2002
    Location:
    South of the USA
    Don't you have 2 inputs? Input 1 is low, input 2 is high. Some of my amps have -10 dB switch.... What is your model?

    Sorry, I haven't seen your signature...150 should have 2 inputs...
     
  4. sturoc

    sturoc

    Joined:
    Dec 12, 2009
    Yes 2 inputs parallel. No Hi or Lo , it is the same on channel 2.
    Remember this is 1st gen Acoustic.
     
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  6. Gaolee

    Gaolee The Fat Violin Supporting Member

    Joined:
    Jan 13, 2010
    I have found that when my Acoustic amps start sounding just a little ratty, they are due for some repairs. Mind you, those repairs are probably the first repairs any of them have ever had, but everything ages after a while. I have run both active and passive basses through an Acoustic 360 stack with good results.
     
  7. Tvrtko

    Tvrtko

    Joined:
    Dec 27, 2002
    Location:
    South of the USA
    Don't you have 2 plugs for each channel? I have 1 gen. 140. It has low and high input for each channel...
     
  8. sturoc

    sturoc

    Joined:
    Dec 12, 2009
    Like I mentioned parallel I opened the amp up just prior to going into "rehab" to have a look at the workmanship, layout myself. Perhaps a prev owner had made them parallel for some reason. Hmmmmmm

    Even with a passive bass still distorts after say '3' on the volume into several different 4 ohm cabs
    Anyhow it is back in the shop for fixing this and also another go thru focusing on transistors.
     
  9. Tvrtko

    Tvrtko

    Joined:
    Dec 27, 2002
    Location:
    South of the USA
    Check caps, specially power caps (I think it's just one). If your power supply does not hold the charge it all gets muddy. Ask Steven Scott. He is on Facebook often. He should be of help.

    https://www.facebook.com/groups/15949664945/

    I love mine 140. It gets nice and fuzzy at about 7... I just got good cab 106 and restored it to almost perfection. Damn, that thing sings!
     
  10. sturoc

    sturoc

    Joined:
    Dec 12, 2009
    Muddy at 7 I could deal with. But it starts pretty soon and volume actually levels off to where it doesn't get any louder while increasing the pot.

    Thanks for the FB tip on Steven.
     
  11. sturoc

    sturoc

    Joined:
    Dec 12, 2009
    Tvrtko

    fyi:
    1st generations are the Original Fat Blue faceplates and big metal control knobs 1967-1971.

    The 140 is the "son of 150B" and is 'gen 2' first made 1972 -76 Black face with narrow blue striping
    Circuitry is very similar though.

    Gen 2 is when the highly sought-after 370 was made(to be my next purchase)
     
  12. Tvrtko

    Tvrtko

    Joined:
    Dec 27, 2002
    Location:
    South of the USA
    Mine is 1972. I found signature in the cabinet: 12/72. Damn thing still sings!
     
  13. garmenteros

    garmenteros Junkyard Scout Gold Supporting Member

    Joined:
    Aug 24, 2008
    Location:
    Dominican Republic
    I own a 370 and have a friends 150b on permanent loan so to say. I gig the 370 and the second input has less output leading to me guess it has a +-5 to 10db cut intended for higher output basses. I used my ernieballs which are quite hot with the 370 without a problem. Plugged them into input 1 without hassle. I can't recall using active basses with the 150 though. Passive guy most of the time. For clean headroom the 370 is the way to go if you're into acoustics. GREAT amps.
     

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